1. Field of the Invention
The present invention relates to a material for forming an insulating film and, more particularly, it relates to an insulating film-forming material that, as a material for an interlayer insulating film in a semiconductor device, etc., can form a coating having an appropriate, uniform thickness and, furthermore, is resistant to cracking and has excellent permittivity characteristics.
2. Description of the Related Art
Conventionally, as interlayer insulating films in semiconductor devices, etc., silica (SiO2) films formed by a vacuum process such as a chemical vapor deposition (CVD) process have been frequently used. Furthermore, in recent years, in order to form a more uniform interlayer insulating film, a coated type insulating film containing as a main component the hydrolysis product of a tetraalkoxysilane, known as a SOG (Spin on Glass) film, has come into use. Moreover, accompanying the higher integration of semiconductor devices, etc., a low permittivity interlayer insulating film containing as a main component a polyorganosiloxane, known as an organic SOG, has been developed.
However, the permittivity of a CVD-SiO2 film, which shows the lowest permittivity among inorganic material films, is on the order of 4. The permittivity of an SiOF film, which has been recently investigated as a low permittivity CVD film, is approximately 3.3 to 3.5, but this film is highly hygroscopic, and there is therefore the problem that its permittivity increases during use.
On the other hand, with regard to organic polymer films showing a permittivity as low as 2.5 to 3.0, the glass transition temperature thereof is as low as 200° C. to 350° C., the thermal expansion thereof is large, and there is therefore the problem that wiring might be damaged. Furthermore, the organic SOG film has the disadvantage that cracks are caused as a result of oxidation by oxygen plasma ashing used for stripping a resist, etc. when forming a multilayer wiring pattern.
Furthermore, since an organic resin containing the organic SOG has poor adhesion to aluminum, aluminum-based alloys, copper, and copper-based alloys, which are used as wiring materials, voids (cavities formed between the wiring and an insulating material) are formed beside the wiring and water is trapped therein, thus causing the possibility of corrosion of the wiring. Moreover, these voids beside the wiring will cause a short circuit between wiring layers if misalignment occurs when opening a via hole for the formation of multilayer wiring, thus degrading the reliability.
Under such circumstances, as an insulating film material having excellent insulation, thermal resistance, and durability, an insulating film-forming coating type composition containing an organopolysiloxane is known (ref. JP-A-2001-329217; JP-A denotes a Japanese unexamined patent application publication). Furthermore, a method for reducing the permittivity by making an organopolysiloxane porous is also known (ref. JP-A-2002-285086). Moreover, a method is known for forming a porous insulating film by synthesizing an organopolysiloxane by use of a silicon compound having a C4 or higher substituent, and decomposing a C4 or higher alkyl group component by heating (ref. JP-A-2000-328004).
However, accompanying the increasingly highly, integrated and multilayered structure of semiconductor devices, etc., there has been a demand for better electrical insulation between conductors, and there has been a desire for an interlayer insulating film material having a lower permittivity and excellent resistance to cracking, heat, and chemical mechanical polishing (CMP).
The above-mentioned known insulating film-forming materials containing a polysiloxane do not have adequate permittivity characteristics, and even if the permittivity characteristics can be reduced by porosification, since the distribution of the pores in the film is uneven, there are the problems that the areas where the pores are unevenly distributed become brittle, and the resistance to CMP becomes poor.